Direct intrathoracic inoculation of Aedes aegypli with wild Central Africa mosquito pools was used for primary multiplication of viruses. The:systematic use of this method permitted the isolation of 4 yellow fever:strains in December 1978. The virus titration during the isolation a mInImal increase of 3 log 10 DL so with this technique as compared to direct inoculation of suckling mice. The strains studied belonged to yellow fever, Zika, West-Nile, Orungo, Chikungunya and Bunyamwera serogroup viruses.